1. Field of the Invention
The present invention relates to an oil pan to be attached to a lower end portion of a machine or like, and more particularly, to an oil pan having an adjusting mechanism for adjusting an oil amount to be sealed in an automatic speed change gear (transmission, called hereinafter) or like.
2. Description of Related Art
In conventional technology, it is known that lubricating oil is sealed in an automatic transmission of an automobile, for example, in which gears or like members for transmitting power is housed for the purposes of realizing smooth driving of gears or like and effectively cooling friction heat generated by the driving of the gear.
As mentioned above, in order to realize the smooth driving of the gear or like and maintain performance for effective cooling of the friction heat, it is necessary to periodically change the lubricating oil and also necessary to maintain sealed amount of the lubricating oil sealed in the automatic transmission. Then, in conventional technology, there has been known a mechanism for adjusting the sealed amount of the lubricating oil sealed in the automatic transmission of an automobile, for example.
Such a conventional sealed lubricating oil amount adjusting mechanism is provided, in order to completely discharge the sealed lubricating oil, with a lubricating oil discharge port formed to the lowest end portion of an oil and a lubricating oil adjusting port for discharging the lubricating oil of an amount more than a predetermined amount of lubricating oil through a tubular-shaped lubricating oil adjusting cylinder. According to this lubricating oil adjusting mechanism, when it is required to exchange the lubricating oil, the exchanging working was performed by the steps of removing a bolt closing the lubricating oil discharge port to thereby discharge whole the amount of the lubricating oil in the automatic transmission, to charge new lubricating oil into the automatic transmission, after closing the lubricating oil discharge port, till the charged lubricating oil overflows the lubricating oil amount adjusting port, and then, closing the lubricating oil amount adjusting port by means of bolt, thus performing the oil exchanging working.
As mentioned above, by forming the lubricating oil amount adjusting cylinder to the oil pan, the sealed amount of oil (or amount of oil to be sealed) in the automatic transmission can be suppressed to an amount less than the predetermined amount, and hence, the amount of oil to be sealed can be precisely adjusted.
However, according to the lubricating oil sealed amount adjusting mechanism of the structure mentioned above, it is necessary to mount or dismount the bolts for closing the lubricating oil discharge port and the lubricating oil amount adjusting port, which may involve complicated working, and in addition, it is necessary to form the lubricating oil discharge port and the lubricating oil amount adjusting port to the oil pan, which may constitute a bar for providing compact structure of the oil pan, and hence, of the automatic transmission, thus providing inconvenience.
In consideration of the above matters encountered in the conventional technology, a lubricating oil sealed amount adjusting mechanism disclosed in Patent Publication 1 (Japanese Patent Application Laid-open Publication No. 2008-25784) is provided with an overflow plug which is detachably mounted to the lubricating oil discharge port. According to this lubricating oil sealed amount adjusting mechanism, when it is required to exchange the lubricating oil, the overflow plug and a bolt closing the lubricating oil discharge port are both removed, and the lubricating oil sealing the automatic transmission is discharged. Thereafter, only the overflow plug is mounted to the lubricating oil discharge port, and the lubricating oil is then supplied. Accordingly, the lubricating oil of the amount more than the predetermined amount can be discharged, thereby adjusting the amount of the lubricating oil to be sealed.
According to the lubricating oil sealed amount adjusting mechanism of the structure mentioned above, the oil exchanging working can be done easily and effectively, thus making compact the structure of the oil pan.
However, according to the lubricating oil sealed amount adjusting mechanism disclosed in the Patent Publication 1, in spite of the above technical merit, it is necessary to mount or dismount the overflow bolt every time of exchanging the lubricating oil, and therefore, it is difficult to keep constant the height level of the front end portion of the overflow plug every time of mounting or dismounting the overflow plug, leading to difficulty of precisely adjusting the amount of the lubricating oil to be sealed. In case of less or much amount of the lubricating oil to be sealed, it becomes impossible to keep constant resistance to be applied to mechanical parts or components such as gears constituting the automatic transmission, and hence, it is difficult to maintain essential performance of the lubricating oil for realizing the smooth driving of the gears or like and effectively cooling the friction heat.